if strcmp(signal, 'off')
    I = std_IQ*randn(M, N) ;
    Q = std_IQ*randn(M, N) ;
    X2 = I.^2 + Q.^2;
    X2max(j) = max(max(X2));

 elseif strcmp(signal, 'on')
    dtau = tau(j) - tau_tilda_m;
    domega = omega(j) - omega_tilda_m;
    I = A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .* cos(domega*T/2 + dphi(j)) + std_IQ*randn(M, N) ;
    Q =- A*L/2 * ro(dtau) .* sinc(domega*T/2 /pi) .* sin(domega*T/2 + dphi(j)) + std_IQ*randn(M, N) ;
    X2 = I.^2 + Q.^2;
    X2max(j) = max(max(X2));
 end